Adolescent obesity is a problem characterized by significant after-effects including altered metabolism of glucose and a predisposition to diabetes mellitus. In order to better understand the metabolic abnormalities associated with adolescent obesity, we will compare the rates of glucose and whole-body protein synthesis and catabolism in morbidly obese and normal adolescents. Whereas weight reduction by calorie restriction is the therapy of choice in obese adolescents, the risk of growth retardation is an undesirable side effect. Therefore, we will also investigate the relationship between the rates of protein turnover and glucose turnover in obese adolescents under different dietary conditions. Since excessive lean body mass is a frequent occurrence among obese adolescents, both the quantities of glucose and protein during the dietary periods will be based on ideal body weight determined by a measurement of total body water. Our studies should clarify whether fat or carbohydrate is the more appropriate source of energy for supporting the growth spurt in obese adolescents receiving hypocaloric dietary therapy. Finally, we will determine if weight reduction in obese adolescents results in a normalization of protein and glucose metabolism.